The development of planar transmission media in the early 1950's had a major impact on microwave circuit and component packaging technology. The engineering of the microwave printed circuit and the supporting analytical theories for stripline and microstrip occurred at a rapid pace. The early years of stripline circuit design were devoted almost entirely to the design of passive circuits such as directional couplers, power dividers, filters, and antenna feed networks. Early implementations were housed in bulky metal housings and connected by coaxial connectors.
To reduce size and weight, case-less and connector-less couplers were developed. These later implementations were sometimes referred to as “filmbrids” and included laminated stripline assemblies bonded together by fusion, or with thermoplastic or thermoset films. Further refinements continued in areas such as the dielectric materials used in these devices and the microwave-circuit fabrication process itself. A historical perspective on the development and applications of microwave integrated circuits, can be found in “Microwave Integrated Circuits—An Historical Perspective”, H. Howe, Jr., IEEE Trans. MTT-S, Vol. MTT-32, pp. 991-996; September 1984; and “Microwave Printed Circuits—The Early Years”, R. M. Barrett, IEEE Trans. MTT-S, Vol. MTT-32, pp. 983-990; September 1984.
Stripline and microstrip components have been integrated for various applications in housings and packages, as well as monolithically on a common substrate. Methods of integration and packaging affect the system interface and installation, as well as the module's ability to handle post-processing temperatures (i.e., post-manufacture of the stripline or microstrip component), and the module's operating thermal management ability (i.e., its heat transfer ability). Common techniques for integrating components call for bonding them together using, e.g., epoxies, adhesives and solder. Leads may be attached to the modules after bonding to provide for signal coupling to external signal sources. Generally speaking, prior techniques of lead attachment have provided for attachment of the leads after bonding.